The present invention relates to terahertz (THz) radiation and more particularly to methods and apparatus for the power enhancement of such radiation.
The THz region (1 THz=33 cmxe2x88x921 or 4 meV) lies in the far infrared spectral range where conventional thermal sources are very weak. For example, a blackbody source at 2,000xc2x0 K. provides less than 1 xcexcW per cmxe2x88x921 of spectral power density for a typical spectroscopy application. A system for the production of multiwatt THz radiation is described in Nature, Vol. 420, Nov. 14, 2002, pp. 153-156. While the production of such high power THz radiation constitutes a significant step forward in the art, even further enhancement, i.e. increase in the THz radiation power for subsequent use in medical diagnostic, security and other similar applications would be highly desirable. Thus, the availability of a method and apparatus that permits increasing the energy of the THz pulse to a value higher than would be available from as single pulse, produced as described in the aforementioned xe2x80x9cNaturexe2x80x9d article, would be highly desirable.
It is therefore an object of the present invention to provide a method and apparatus that permits enhancement of THz radiation to an energy level higher than that available from a single THz pulse.
According to the present invention there are provided a method and an optical mode based apparatus that permit enhancement of the energy level of THz radiation. Such an apparatus comprises a cavity defined by a pair of facing mirrors oriented to receive and reflect a THz radiation pulse derived from an electron beam comprising a series of short electron bunches such that the interval between subsequent electron pulses or bunches in the beam matches the time it takes for the optical mode (mirrors) to return a reflected THz photon pulse to its point of origin where it encounters a subsequent electron bunch acquiring energy therefrom. Enhancement of the THz radiation occurs through the encounter of the reflected THz radiation pulse and an incoming newly generated electron pulse with energy being transferred from the electron pulse to the THz radiation photon pulse. An apparatus comprising such a pair of facing mirrors that provides multiple reflection of photon pulses therebetween for several synchronized intervals and permits removal of the enhanced (higher energy) THz radiation is also described.